Aircraft landing system employing lobe switching of radio beams



R. M. SMITH v AIRCRAFT LANDING SYSTEM EMPLOYING July 4; 195o 21E-,14,351

Y LOBE SWITCHING OF RADIO BEAMS I Filed Jan. 3. '1940 2 Sheets-Sheet l.w IL

JUIY'4, 1950 R. M. SMITH 2,514,35l

AIRCRAFT LANDING SYSTEM EMELOYING LoBE swITcx-IING oF RADIO BEAMs FiledJan. s, 1940 2 sheets-sheet z AAAAAA Vvvvvvv AAAAA Quorum Patented July4, 1950 AIRCRAFT LANDING SYSTEM EMPLOYING LOBE SWITCHING F RADIO BEAMSRogers M. Smith, Merchantvill, N. J., asslgnor to Radio Corporation ofAmerica, a corporation of Delaware Application January 3, 1940, SerialNo. 312,273 y 12 claims. l

'I'his invention relates to an apparatus for and a method of the landingof aircraft, and more craft guiding path is established by a pulsetransmitter so arranged that radiated pulses are reected by theaircraft.

Numerous radio systems have been proposed for the landing of aircraft.In one such system overlapping radio frequency elds establish a runwaylocalizer path which coincides withthe runway of the landing field, Theangle of radiation of these elds is so arranged that an equal signalglide path may be followed by the craft for landing. Furthermore, insystems of this type one or more boundary or distance markers areprovided. These markers provide suitable indications of the distance tothe landing eld.

Another system has been suggested in which a radio transmitter isoperated on the aircraft. Signals from this transmitter actuate a pairof directional receivers, a boundary marker receiver and a glide pathreceiver. Signals derived from the three receivers are used to modulatea broadcast transmitter, Signals from the broadcast transmitter arereceived on the airplane to provide suitable indications of the attitudeof the plane with respect to the runway.

While the foregoing systems may be used in conjunction with properlyequipped aircraft, they are not well suited to aircraft which are notprovided with one or more special receivers, perhaps a transmitter, andindicating instruments.

It is an object of the present invention to provide means for indicatingthe position of an aircraft with respect to a runway and its distancetherefrom. It is another object to provide means whereby a pulsetransmitter may be used to establish a beam so that aircraft flying inthe beam reect pulses which indicatethe position and distance of theaeroplane with respect to a reference line. An additional object is toprovide an apparatus for and a method of advising the operator of anaircraft of its position whereby an instrument landing may be effected.A still further object is to provide means for establishing an aircraftlanding pathso arranged that reected signals indicate the position ofthe craft and for relaying this/information to the operator of the`craft by means of a second radio transmitter.

The invention will be described by referring to the accompanying drawingin which Figure `1 indicates the. radio transmitter and receivingapparatus, Figure 2 indicates the radio receiver which is used on theaeroplane, and Fig- I specifically to a radio system in which an airlure 3 is a schematic diagram of a keyer and modulator for the antennaarray.

A pulse transmitter I and a pulse receiver 3 are connected to an antenna5. The antenna 5 is mounted on a reflecting surface 'l and is preferablyof a length long compared to the transmitted wave length. The pulsetransmitter and pulse receiver are connected respectively to horizontaland vertical deecting electrodes 9 and I I, respectively, of a cathoderay tube I3. The cathode ray tube is used as a distance indicator.Inasmuch as the details of this type of system are well known to thoseskilled in the art, no detailed description is necessary. For the sakeof convenience, reference is made to U. S. Patent 2,401,717 which issuedon the application of Wolff and Hershberger, Serial No. 184,354, ledJanuary 11, 1938, entitled Signaling System. Reflecting antennas I5 andIl are located on either side of the main antenna 5. A second pair ofreflecting antennas i9 and 2i are located above and below the mainantenna 5. These antennas are connected to a. keying device 23 and to akeyer controller 25. The keyer device and keyer controller are soarranged that the reector antennas are successively connected wherebythe beam from the main antenna 5 is successively directed to the rightand left and above and below its normal position. The overlappingportion of the fields forms a glide and localizer path for aircraft.

The switching device 25 is also connected to the receiver 3 and to twopair of filters and rectifiers 2l. l The output of each pair of filtersand rectiers is differentially applied to a crossed pointer indicator2Q. The switching device 25 is also connected to four filters 3l, 33, 35and 31 which may be omitted by using the receiver filter 2l. The severalfilters 3|, etc., are connected to a second transmitter 39. Thistransmitter and modulator may be of the type now employed forcommunicating with aeroplanes or for broadcasting weather reports. Inaddition to the lters 3i, 33, 35, 3l, the transmitter and modulator 39has connected to it a microphone 4I and an adjustable frequencyoscillator d3. The oscillator frequency may be varied by a variablecapacitor i5 or the like which is coupled by means of a link 4l to alever and pointer 49 which is used to follow the distance indications ofthe cathode ray tube I3.

In the aircraft radio receiver, a conventional instrument of thesuperheterodyne or radio frequency type may be employed, the outputbeing applied through a filter 5I to telephone receivers 53. If visualindications are desired, the receiver 3 output may also be applied totwo pairs of filters and rectifiers 55 and 51, the output of each pairbeing differentially connected to a crossed pointed indicator 59. Fordistance indication the output of the receiver is connected to anadditional filter and rectifier 6I which is in turn connected to adistance indicator 63' which is preferably a frequency indicatorcalibratedv in terms of distance as will hereinafter appear. Onesuitable frequency meteris disclosed inthe copending application ofRoyden C. Sanders, Jr., Serial No. 248,577, filed December 30, 1938, forFrequency Meters, which is now U. S. Patent 2,228,367.

The operation of the system is as follows:

The pulse transmitter radiates ultra high frequency energy during pulseintervals of the order of one tenth to one half of a micro-second' at arepetition rate of the-order of v20,000 pulses per second. -If none ofthe refiector antennas were energized or connected the long wave antennawould establish a sharply defined beam 'of energy which would bereflected by an approaching airplane 65, If, by way of example, theantenna I5 is keyed by a distinctive signal, the radiated beam 61 willbe directed to the right. If the antenna |1 is energized, the beam59Willbe directed toward the left. In a like manner by energizing theantennas |9 and 2 I, the beam will be reflected respectively downward toa position indicated by the reference numeral 1| and upwardly to theposition indicated by the reference numeral 13. The intersection of thefour radiation patterns 61, 29, 1| and 13 corresponding to thesuccessive positions of the beam in the four quadrants will provide aglide path for the approaching craft. Thel refiected signals, if thecraft is on the guide path will contain equal amounts of the fourdistinctive signals which appear as modulations on the radio beamcarrier wave.

The demodulated products of the thus reflected and received signals willact equally and oppositely in pairs on the indicator pointers of theinstrument 29. At the same time the reflected signals will indicatedistance in-the cathode ray tube I3. The distance indication is producedby initiating the horizontal scanning of the cathode ray in synchronismwith the transmission of the outgoing pulses. The vertical defiection ofthe ray, caused by the refiected signals indicates the distance of therefiecting object as a function of the time required for the pulse totravel from the transmitter to the object and back to the receiver.

Thus, the position of the aircraft on the guide path and its distancelfrom the transmitter are indicated to an observer at the groundstation. In the event that the aircraft is off the course and withinanyone or more of the radiationpatterns 61, 69, 1|, 13, a distinctivemodulation signal will beA received. The received signal will cause thecrossed pointer device 29 to indicate Whether the aircraft is tothe leftor right or up or down with respect to the desired glide path.

While all of the foregoing information may be transmitted to theoperator of the aircraft by means of speech signals applied to themicrophone 4|, it is desirable to indicate automatically to theaircraft-operator the position of the craft with respect to the glidepath. This may be done by modulating the second transmitter 39 ntransmitter I A visible indication of the distance of the craft isobtained automatically by following the horizontal deflection of thecathode ray -beain by means of a pointer 49. This pointer is connectedto the variable element 45 of the oscillator I3 whereby a distinctivefrequency is transmitted as a function of the distance indication. Thisdistinctive frequency is preferably sufficiently removed from the othermodulation frequency so that it may be separated therefrom and appliedto the frequency type indicator 63 which is calibrated in terms of anysuitable units indicating distance.

One other type of information may be supplied to indicate the rate ofapproach of the craft. This information may be obtained by observingtherate of change of the reflected pulses as described in detail in thecopendingl application of Smith Serial No. 293,133, filed Septem-ber 1,1939, now Patent No. 2,492,012, granted December 20, 1949. Thisinformation may be conveyed lto the aircraft operator by means of themicrophone 4I, or it may be applied in a manner similar to that in whichthe distance indication is transmitted automatically.

While it does not appear necessary to Vdescribe the method of applyingthe distinctive modulation of the radio beam carrier, in view of theknown systems for directing aircraft, reference is made to D. S. BondsU. S. Patent 2,238,965, in which such methods are described. It shouldbe understood that the distinctive modulation may be arranged in pairsof complementary telegraphic systems such as A--N and E-T. Thetelegraphic signals are preferably modulated by audio-frequencies of theorder of 60, 70, and cycles per second whereby the signals may bereadily filtered and applied to the indicating meters. It should beunderstood that the telegraphic characters may be entirely omitted infavor of the distinctive frequency method of marking the respectivebeams, as shown in Fig. 3.

Referring to Fig. 3, the keyer 1| is driven by a motor 13 so that theantennas |5, I1, I9 and 2| are successively grounded, whereby theybecome reflectors. As each reflector antenna is grounded, currents areinduced from the central antenna current. The induced currents areapplied through capacitors 15, 11, 19 and 8| to rectifiers 83, 85, 81and 89, respectively. These currents are rectified by the rectifier towhich they are applied. The rectified currents are used to biaspositively the control grids of the amplifiers 9|, 93, 95 and 91,respectively. Since these amplifiers are normally biased to cut-off,they are incapable of transmitting modulating currents from the fourlocal oscillators 99, IDI, |03 and |05, which are operated at differentfrequencies.

As each of the antennasv is successively energized and the currentstherefrom rectified to bias the amplifiers into an operating condition,the distinctive modulation frequency currents are applied through theamplifier |01 to the modulator |09 which is connected to the pulse Theoutput from the pulse transmitter is applied to the central antenna 5 sothat the resultant beam is distinctively modulated and at the same timemoved up or down, or right or left by the grounded reflector, toestablish four regions marking the-glide path for the air plane.

No attempt has ybeen made to describe in detail the biasing voltages andcircuit connections of the modulator and keyer system, inasmuch as acomplete description of the mode of operation will be found in Bond U.S. Patent 2,238,965.

Thus, the invention has been described 'as an apparatus method forlanding aircraft. A pulse transmitter is used to establish overlappingbeams to thereby form a glide path. The reflected signals indicate theposition 'and distance of the craft with respectI lto the transmitterand glide path. The information, thus obtained, may be relayed to theaircraft operator by a second transmitter whose signals are received bya conventional receiving device. 'I'he receiving device may includevisual indicators.A This system has the distinct advantage of placingall of the heavy equipment on the ground and it employs the conventionalreceiver which is generally installed on aircraft.

I claim as my invention:

1. An aircraft instrument landing system including a radio transmitterfor transmitting pulses, means for radiating said pulses in the form ofa beam, means for directing said beam up and down and right and leftsequentially so that overlapping portions of said directed beam form aglide path, means for modulating said beam in each of its respectivepositions with signals of distinctive frequencies, a receiver responsiveto said modulated beam signals after said signals are reflected from anaircraft in said beam, filters respectively responsive to saiddistinctive modulation connected to said receiver for selecting saiddistinctive signal modulation, a second radio transmitter, and meansconnecting said second transmitter and said receiver for applying saidselected distinctive modulation sig- Vnals to modulate said secondtransmitter for transmission of said modulation signals to saidaircraft.

2. In the system described in claim -1 an indicator connected to saidfilters for indicating the relative strengths of the signals reflectedby said beam in its respective up-down and left-right positions.

3. The system described in claim -1 including a receiver located in saidaircraft responsive to the signals from said second transmitter forindicating the position of the aircraft reflecting the signals from saidpulse transmitter, said receiver comprising filters responsive to saiddistinctive frequency modulation signals, respectively, and an indicatormeans connected to said filters for comparing the signal strength of thefilter outputs.

4. An aircraft landing system including, in combination, a pulsetransmitter, means for radiating said pulses in a beam shape path, meansfor directing said beam up and down and left and right sequentially sothat an overlapping portion forms a predetermined glide path, meansoperated in synchronism with said beam directing means for furtherdistinctively modulating said beam in each of its respective positions,a receiver responsive to pulses reflected by an aircraft in said beam,selector means connected to said receiver and selectively responsive tosaid distinctive reflections, indicators connected to said receiver andto selector means for indicating respectively the time between radiationand reception of a reflected pulse and for indicating the ratio ofreflected signals from said beam in its respective up-down andleft-right positions, a

second transmitter, and means for applying the received reflecteddistinctively modulated signals to modulate said second transmitter.

5. In a system such as described in claim 4 means for generating thesignals which vary as a function of the time between radiation of apulse and its reception after reflection, and means for modulating saidsecond transmitter with said signals.

6..'In/a system of the type described in claim 4, a. receiver responsiveto the signals from said second transmitter located on the aircraftreflecting said pulse signals fory indicating to the operator of theaircraft its position with respect to said glide path.

7. In a system of the type described in claim 4, means for generatingthe signals whichvary as a function of the time between radiation of apulse and its reception after reflection and means modulating saidsecond transmitter with said generated signals so that its signalsinclude distance information and a receiver selectively responsive tothe signals from said second transmitter located on thev aircraftreflecting said pulse signals for indicating to the operator of theaircraft its position with respect to said glide s path andits distancefrom said radiationmeans.

8. An aircraft instrument landing system including a pulse transmitter,means for radiating said pulses in a sharply defined beam, means fordirecting said beam up and down and right and left so that the resultantbeam positions overlap and form a landing guide path for aircraft, meansfor modulating said beam in each of its respective positions with adistinctive signal different from that of all other positions, areceiver responsive to said pulse signals reflected froman approachingaircraft, a distance indicator connected to said receiver and operatedas a function of the time between transmission and reception of areflected pulse, means connected to said receiver and responsive theretoto reproduce said distinctive signals at relative amplitudes dependingupon the strengths with which they are received, a second transmitter,means applying said reproduced signals to said second transmitter tomodulate the radiations from thelatter, a local adjustable frequencyoscillator connected to said second transmitter and including means forvarying the frequency as a function of the distance indicated on saiddistance indicator.

9. An instrument landing system for aircraft comprising means forradiating pulses in a radio beam, means for directing vsaid beam up anddown and right and left to form an overlapping region, means fordistinctively carrier `wave modulating said beam in each of itsrespective positions, means for receiving said distinctively modulatedbeams after reflection from an aircraft, said receiving means includingmeans for selecting the distinctive modulations, means for radiating acarrier wave to the aircraft' reflecting the pulses, means formodulating said carrier wave with distinctive signals corresponding tosaid selected signals, means for receiving said modulated carrier on tleaircraft reflecting the pulses, means for demodulating said receivedcarrier to obtain said distinctive signals, and means for comparing saiddistinctive signals to indicate the position of said aircraft as afunction of said distinctive signals of said carrier.

10. An instrument landing system for aircraft comprising means forradiating pulses in a beam, means for directing said beam up and downand right and left to form an overlapping region, means operatingsynchronously with said beam directing means for distinctively carrierwave modulating said beam in each of its respective v5 positions bysignals of different frequencies.

means for receiving said distinctively modulated beams after reflectionfrom an aircraft, said receiving means including means for selecting thedistinctive modulation signals, means for radiating a carrier wave tothe aircraft reflecting the pulses, means for modulating said carrierwave with distinctive signals corresponding'to said seright and left toform an overlapping region means for distinctively carrier wavemodulating said beam in each of its respective positions, means forreceiving said distinctively modulated beams after reflection from anaircraft, said receiving means including means for selecting thedistinctive modulations, means for comparing the selected signals toindicate the position of the craft with respect to said overlappingregion, means for radiating a carrier wave to the aircraft reecting thepulses, means for modulating said carrier wave with distinctive signalscorresponding to said selected signals, means for receiving saidmodulated carrier on the aircraft reflecting .the pulses, means fordemodulating said carrier to obtain said distinctive signals, and meansfor indicating the position of said aircraft as a function of saiddistinctive signals of said carrier.

12. An instrument landing system for aircraft comprising means forradiating pulses in a beam, means for directing said beam up and downand right and left to form an overlapping region, means fordistinctively carrier wave modulating said beam by audio frequencysignals in each of its respective positions, meansfor receiving saiddistinctively modulated beams afterv reflection from an aircraft, saidreceiving means including means for selecting the distinctivemodulations, means for comparing the relative magnitudes vof theselected signals to indicate the position of the craft with respect tosaid overlapping region, means for timing the interval between theradia- 'tion of a pulse and its reception after reflection to indicatethe distance of the aircraft reflecting said pulse, `means for radiatinga carrier wave to the aircraft reflecting'the pulses, means formodulating said carrier wave with distinctive signals corresponding tosaid selected signals, means for receiving said modulated-carrier on theaircraft refiecting the pulses, -means for demodulating said carrier to'obtain said distinctive signals, and means for indicating the positionof said aircraft as a function of said distinctive `signals of saidcarrier.

ROGERS M. SMITH.

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